Pipelines are widely used for the transport of oil, gas, water etc. Pipelines may be used onshore as well as offshore. Usually these pipelines are single layer pipes made from metal, e.g. steel, copper, lead etc. For the transport of oil and gas usually steel pipelines are used. In the case of flexible pipelines, often a multilayered pipeline is used, comprising a flexible polymer pipe surrounded by several layers of helically wound metal structures.
Blockages in pipelines, especially in subsea pipelines and pipelines in cold climate area's, may cause substantial damage in the form of production downtime. The blockages are typically caused by wax and/or hydrate formation, possibly resulting in gel formation in the oil. This happens especially when the flow in the pipeline is interrupted, followed by cooling of the oil. Quite often it is difficult or even impossible to remove these blockages by conventional methods, particularly when the blockage is located at a substantial distance from an accessible end of the pipeline. Increasing the pressure would often require pressures above the pipeline specification, which is clearly undesired.
In U.S. Pat. No. 3,780,751, a method is described for restoring the flow in a blocked pipeline by injection fluid at several points in the pipeline.
In U.S. Pat. No. 6,122,791, a retrievable pig is described for the cleaning of pipelines and the removal of blockages.
In WO 99/25495, a pipe cleaning pig provided with a tow cable.
In U.S. Pat. No. 6,939,082, a vehicle is described that moves along a subsea pipeline, the vehicle providing hot seawater for circulating over the outer surface of the pipeline in order to melt hydrates and/or paraffin deposits.